Series X and Series S
They both play the same games.
But.
The S has an output of upto 1080
The X has an output of upto 4k
(Won't matter if you do t have a 4k TV)
The S has a slightly lower GPU speed which basically means that some game that run at 60fps on Series X won't run at 60fps on Series S. But, 30fps is fine for most games, unless high end competition FPS.
The original Series X has a disc drive, series S doesn't so digital games only on Series S.
Series X has a bigger memory to store games.
Basically.
If you've got a 4k TV - series X
If you want to buy physical games - Series X
If you've got a hd TV 1080p and you're only going to use Gamepass. Series S
Series S and Gamepass is amazing tbh
As for last ability.. well, they've been out a good while already, I wouldn't be surprised if redesigns and new consoles are announced before your 5 years are up.
Tbf. I got the Series S and Gamepass because I wondered if they'd announce a pro version etc after a couple years. But I've been delighted with it. £250 and it's awesome.